Carbon coatings are applied on metal substrates to impart the substrate with surfaces having unique properties such as low friction coefficient, high corrosion resistance and high electroconductivity. Carbon coating films can be deposited electrochemically on a conductive substrate. A method for electrochemically depositing such carbon films is disclosed in H. Kawamura and Y. Ito, Journal of Applied Electrochemistry, 30:571 (2000). The method comprises electrochemically reducing carbonate ion (CO32−) into elementary carbon to be deposited on the surface of a substrate acting as cathode in a molten salt electrolyte bath containing carbonate ion.
This method is advantageous compared with other known methods such as chemical vapor deposition (CVD) or physical vapor deposition (PVD) in many respects including, for example, high throwing power comparable to electrolytic metal plating, simple operation and no need of complicated apparatus. However, the method tends to produce a carbon coating film which is not dense and consisted of porous aggregate of carbon particles.
A need exists, therefore, for a novel method for electrochemically depositing carbon films on a conductive substrate which can eliminate or ameliorate the defects of the known methods while retaining most of advantages thereof.